This invention relates to optical coupler systems and to methods of assembling such systems.
Optical systems today commonly have a need for optically coupling one solid optical element with another. Normally, it is important that there be little, if any, loss of radiant energy at the interface of the two elements. For example, where light is transmitted through a series of structurally independent optical fibers or waveguides, any loss of radiant energy between adjacent elements is cumulative and can thus quickly limit light transmission efficiency. Similarly, where optical devices have multiple layered elements, such as where scintillants are coupled with photomultipliers, or where the ends of optical waveguides are coupled with transducers such as photodetectors, it is equally important that coupling efficiency be maximized.
Due to the fact that optical fibers are extremely small, it is difficult to couple the elements together by direct contact with any appreciable degree of coupling efficiency. In practice it is too difficult to form and align such fibers with their mutually confronting surface both planar and in parallel, flush abutment. This can be even more difficult to achieve where the mating surface of optical elements are curved.
This has lead to the development of structurally independent coupling materials which are interposed between confronting surfaces of the optical elements. For example, in U.S. Pat. No. 3,457,000 an optically clear adhesive is suggested to improve coupling efficiency. The July/August 1975 issue of the Bell System Technical Journal has suggested the use of a gel. Various fluids have also been proposed. For example, in U.S. Pat. No. 3,768,146 a drop of glycerine having an index of refraction of 1.47 is used for coupling together two optical fibers having a fiber core with an index of refraction of 1.62. In U.S. Pat. No. 3,963,308 an index matching liquid such as cinnemaldehyde or a silicon polymer solid is proposed. U.S. Pat. No. 3,933,678 teaches an organosilicon, greaselike compound having good light shear stability for assembling a scintillant to a photomultiplier. In United Kingdom Pat. No. 1,017,354 glass is used as a structurally independent element coupling two optical fiber ends together. Variable couplers having a changeable index of refraction have also been suggested in U.S. Pat. No. 3,976,358 in the form of a semiconductive material GaAs or AaAlAs. In the foregoing cases mechanical holding means have been required for holding the optical elements and coupler together as an assembly.
Though the just described optical couplers have been capable of coupling together two or more optical elements, they have not been without manifest deficiencies and limitations. For example, where the coupler is a rigid material the optical elements or the coupler itself may need to be momentarily heated during assembly to cause a flow and melting together of adjacent materials. Without such the provision of the structurally independent coupler, which actually serves to double the number of interface junctions, can sometimes actually decrease coupling effectiveness. Where liquids are utilized they can be difficult to apply with efficiency and reliability. The use of greases and adhesives is also difficult to use in properly measured quantities without leaving air gaps or waste.
Accordingly, it is a general object of the present invention to provide an improved optical coupler system.
Another general object of the present invention is to provide an improved method of assembling an optical coupler system.
More specifically, it is an object of the invention to provide an optical coupler system by which coupling may be effected without substantial loss of radiant energy from the coupler assembly.
Another object of the invention is to provide an optical coupler system in which an optical element can be repeatedly coupled and uncoupled without coupler destruction or injury.
Another object of the invention is to provide a method of assembling an optical coupler system of the type described which may be easily practiced without need for precision formation or alignment of the interfacing surfaces of the optical elements.